I guess this depends on your setup, but what you might do is keep the images for, say 15 minutes and then delete them. You could do this with a routine in your image-generating CGI script (as I understand your setup), or (better for so many reasons) you could write a cron job that deletes files that are 15 minutes (or whatever value makes sense) old or older. Perl's -M filetest returns the amount of time, in days, since the file was modified. Assuming nothing's gonna change your files other than creation, the value of -M file will tell you how long since file was created.

Here's a suitable cron script ... UNTESTED, so check it over =)

#!/usr/bin/perl -w

# delold.pl  -- deletes files older than a certain # of minutes

use strict;

# this is a bit clunky; ideally you'd use the Getopt::Std module, but 
+hey.

my $maxage = shift || 15;  #you can call the script with "delold.pl 20
+" and it will delete files that 
                #haven't been modified for 20 minutes.

my $dir = shift || "/usr/www/images/temp"; # or wherever makes sense

opendir DIR, $dir or die "Can't open $dir: $!\n";

while (my $file = readdir DIR) {
    next unless -f "$dir/$file"; # skip directories, etc.
    unlink "$dir/$file" if -M "$dir/$file" > ($maxage / 1440);
}
closedir DIR;
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Philosophy can be made out of anything. Or less -- Jerry A. Fodor